public class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if(root == null) {
            return 0;
        }
        if(root.left != null && root.left.left == null) {
            if(root.left.right == null) {
                return root.left.val + sumOfLeftLeaves(root.right);
            }
        }
        return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
    }
}